1. Field of the Invention (Technical Field)
The present invention relates to control logic speed control of turbine systems.
2. Background Art
Note that the following discussion refers to a number of publications by author(s) and year of publication, and that due to recent publication dates certain publications are not to be considered as prior art vis-a-vis the present invention. Discussion of such publications herein is given for more complete background and is not to be construed as an admission that such publications are prior art for patentability determination purposes.
Turbine engines such as microturbines or xe2x80x9cturbogeneratorsxe2x80x9d typically comprise three main sections: a compressor, a combustor, and a power turbine. In general, compressed air is mixed with fuel and burned under constant pressure conditions to produce a hot gas that expands through a turbine to perform work. A portion of the work compresses air while the remaining portion is available for other use, e.g., mechanical drive, electrical generation, etc. Electrical generation is achieved, for example, through use of a shaft mounted in a permanent magnet/stator assembly.
Some turbine power generators are fitted with a recuperator, which recuperates heat from exhaust gas exiting the power turbine. The recuperated heat is often used to pre-heat compressed air prior to combustion. By recovering heat from the exhaust gas and putting it back into the system prior to the combuster, less fuel is needed to sustain a given turbine operating temperature.
Often a recuperated turbine power generator has two distinct modes of operation: normal mode and bypass mode, in which compressor air is directed from an inlet duct to an outlet duct without entering the recuperator. In by-pass mode, exhaust heat does not pre-heat compressed air prior to combustion. In by-pass mode, a turbine generator may still achieve full power, but at a higher fuel consumption when compared to normal mode operation. In by-pass mode, the temperature of the recuperator rises as long as no fluid and/or gas are available in cold-side passages of the recuperator to receive heat from the exhaust gas passing through the hot-side passages of the recuperator. Bypass also comprises bypassing the recuperator and the turbine, for example, a recuperator and turbine bypass valve may direct a fraction of the total air away from the recuperator and turbine. Where the recuperator and turbine are bypassed or partially bypassed, the overall effect is to load down the turbine.
For recuperated turbine electrical generators, turbine speed depends on load and operational mode, e.g., normal and recuperator by-pass modes. For example, if a large load is dropped quickly, then turbine speed increases rapidly, which may harm the generator absent an overspeed cut-off. If a large load is dropped slowly, then turbine speed may be uncontrollable for several minutes until, for example, the recuperator cools down. Alternatively, or in combination with overspeed, overvoltage may occur in electrical generators. Of course, in mechanical generators, at least one condition analogous to overvoltage may occur, which may be potentially detrimental.
The following patent discloses use of a valve system for controlling turbine operation.
U.S. Pat. No. 4,761,957, entitled xe2x80x9cIndirectly Heated Gas Turbine Engine,xe2x80x9d to Eberhardt et al., issued Aug. 9, 1988 (""957 Patent), discloses a three valve system for controlling turbine operation: (i) a modulating bypass trim valve to control hot gas flow to the turbine; (ii) another modulating valve to control pressure drop for efficient control of the turbine; and (iii) a dump valve or surge control valve in the event of rapid engine decelerations where the pressure of the air in the recuperator is higher than the output of the compressor. The ""957 Patent also discloses use of a compressor bleed valve during start-up to prevent surge, choke and stall.
A need exists for better methods to control all types of turbine power generators.
In one embodiment, the present invention comprises control logic for controlling a turbine in response to a change in load. A change in load comprises, for example, but is not limited to, a turbine user scheduled change, an unexpected load change, and/or a demand load change that is unexpected, scheduled, and/or otherwise. Of course, in some instances, for example, but not limited to, in an emergency shut down situation, the control may not necessarily be implemented in response to a change in load. In other instances, some other condition may activate and/or reset control. In one embodiment, the inventive control logic comprises at least one input for inputting at least one turbine parameter and at least one circuit for comparing the at least one turbine parameter to at least one turbine control criterion wherein the at least one turbine control criterion comprises a member selected from the group consisting of activation criteria and reset criteria and wherein the at least one circuit outputs a control signal. A turbine parameter comprises a parameter related to the operation of a turbine; therefore, a turbine parameter comprises, for example, but is not limited to, parameters such as: gas flow, mass, pressure, volume, temperature, composition, and concentration; compressor speed and acceleration; turbine speed and acceleration; rotor speed and acceleration; fuel flow, mass, volume, composition, concentration, temperature, pressure, and energy value (e.g., btu); bearing parameters; shaft parameters; load and/or unload parameters; equipment temperature; an event; a time; number of events; a duration of time; and the like. A turbine parameter optionally comprises a derivative of another turbine parameter, for example, acceleration comprises the time derivative of speed. Of course other derivatives based on distance, other measures and/or parameters are within the scope of the present invention. The invention, however, is not limited to derivatives that are input as turbine parameters because according to the present invention, logic comprising a circuit for determining a derivative is within the scope of the present invention. Again, such a derivative optionally comprises derivatives based on time, distance, other measures and/or parameters and are within the scope of the present invention.
According to this embodiment, a turbine control criterion comprises a criterion related to operation of a turbine, including, for example, a criterion related to a turbine parameter. In such an embodiment of the inventive control logic, for example, but not limited to, a criterion functions as an activation criterion and/or reset criterion. In one embodiment, an activation criterion comprising an unload criterion is used. In another embodiment, a reset criterion comprising a time, a time delay and/or event is used. Of course embodiments comprising both are within the scope of the present invention. Therefore, according to such an embodiment of the present invention, an activation criterion controls activation and a time and/or event controls reset. In such an embodiment, the invention control optionally comprises a timer and/or event counter wherein activation and/or a turbine parameter optionally interact with the timer and/or event counter.
In an embodiment of the present invention, the control logic outputs a control signal that comprises a valve control signal. In such an embodiment, the valve control signal optionally controls a bypass valve. According to the present invention, a bypass valve operates to bypass gas from one section of a turbine generator to the environment and/or to another section of a turbine generator. For example, but not limited to, bypass of gas from a compressor; before a turbine; before a recuperator; from a turbine; from a recuperator; from a compressor and before a combuster; before a combuster; after a combuster; and the like. In an embodiment where comprising bypass of gas from a compressor, the bypass optionally comprises means to bypass at least 1% of the total gas flow from the compressor. In such an embodiment, the gas flow bypass optionally ranges from approximately 0% to approximately 100%, preferably from approximately 1% to approximately 50% and most preferably from approximately 1% to approximately 25%. In one embodiment, a bypass valve bypasses approximately 15% of the gas flow from the compressor, when activated and approximately 0% when reset. While a valve is suitable, other means of bypass are within the scope of the present invention.
In one embodiment, the present invention comprises control logic for controlling a turbine comprising at least one input for inputting a turbine speed value, a turbine speed set-point criterion, a speed activation criterion, a speed reset criterion, an turbine acceleration load criterion, and an turbine acceleration unload criterion; and at least one circuit for determining a speed error value from the turbine speed value and the turbine speed set-point and a turbine acceleration value from the turbine speed value and for comparing the turbine acceleration value to the turbine acceleration load criterion, the turbine acceleration value to the turbine acceleration unload criterion, the speed error value to the speed activation criterion and the speed error value to the speed reset criterion wherein the at least one circuit outputs a control signal. This embodiment is optionally useful for turbine generators operated in stand-alone mode.
In one embodiment, the present invention comprises control logic for controlling a turbine comprising: at least one input for inputting a turbine speed value, a turbine speed set-point criterion, a speed activation criterion, and a speed reset criterion; and at least one circuit for determining a speed error value from the turbine speed value and the turbine speed set-point and for comparing the speed error value to the speed activation criterion and the speed error value to the speed reset criterion wherein the at least one circuit outputs a control signal. This embodiment is optionally useful for turbine generators operated in grid mode.
The present invention also comprises an inventive method for controlling a turbine. In one embodiment, the invention method for controlling a turbine in response to a change in load comprises the steps of: inputting at least one turbine parameter; comparing the at least one turbine parameter to at least one turbine control criterion wherein the at least one turbine control criterion comprises a member selected from the group consisting of activation criteria and reset criteria; and outputting a control signal based on the comparing step. The method optionally comprises use of an activation criterion comprising an unload criterion; use of a reset criterion selected from the group consisting of time, time delay and event; and/or combinations thereof. In one embodiment, the method comprises outputting a valve control signal, for example, to a bypass valve wherein the bypass valve causes, for example, bypass of at least 1% of the total gas flow from a compressor. The method optionally routes the gas back to the turbine generator and/or dumps it to the environment and/or other sink.
The inventive method optionally comprises at least one turbine parameter that comprises a derivative of another turbine parameter, such as, but not limited to, a time derivative. The inventive method optionally comprises at least one circuit that further comprises a circuit for determining a derivative of a turbine parameter, such as, but not limited to, a time derivative.
The invention also comprises a method for controlling a turbine comprising the steps of: inputting a turbine speed value, a turbine speed set-point criterion, a speed activation criterion, a speed reset criterion, a turbine acceleration load criterion, and a turbine acceleration unload criterion; determining a speed error value from the turbine speed value and the turbine speed set-point and a turbine acceleration value from the turbine speed value; comparing the turbine acceleration value to the turbine acceleration load criterion, the turbine acceleration value to the turbine acceleration unload criterion, the speed error value to the speed activation criterion and the speed error value to the speed reset criterion; and outputting a control signal based on the comparing step. This method is optionally useful for controlling a turbine in a stand-alone mode.
The invention also comprises a method of controlling a turbine comprising the steps of: inputting a turbine speed value, a turbine speed set-point criterion, a speed activation criterion, and a speed reset criterion; determining a speed error value from the turbine speed value and the turbine speed set-point; comparing the speed error value to the speed activation criterion and the speed error value to the speed reset criterion; and outputting a control signal based on the comparing step. This method is optionally useful for controlling a turbine in a grid mode.
The invention also comprises inventive control logic for controlling a turbine, for example, but not limited to, control in response to a change in load comprising: means for inputting at least one turbine parameter; and means for comparing the at least one turbine parameter to at least one turbine control criterion wherein the at least one turbine control criterion comprises a member selected from the group consisting of activation criteria and reset criteria and wherein the at least one circuit outputs a control signal. Means for inputting optionally comprises digital and/or analog devices, fluid and/or gas devices, pressure and/or temperature sensitive devices, software driven devices, electromagnetic devices, electrical devices and/or mechanical devices. Means for comparing optionally comprises digital and/or analog devices, fluid and/or gas devices, pressure and/or temperature sensitive devices, software driven devices, electromagnetic devices, electrical devices and/or mechanical devices. One of ordinary skill in the art of control systems would understand how to configure such input means and comparing means based on the aforementioned and other devices.
A primary object of the present invention is to control turbine speed.
A primary advantage of the;:present invention is effective control of turbine speed.
A secondary advantage of the present invention is optional use of a low cost on/off valve.
Other objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and will become apparent to those skilled in the art upon examination of the following, and/or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.